This invention relates in general to optical communication and, in particular, to wavelength selection switches for optical application.
As multiple forms of communication traffic continue to place increasingly heavy burdens on fiber optic networks, users are looking for innovative ways to push more data through existing fiber. Dense Wavelength Division Multiplexing (DWDM) offers a state-of-the art alternative for increasing the transmission capabilities of fiber networks using optical technology. DWDM allows multiple streams of data to share a common communications channel by placing data streams onto different wavelengths. The result is a dramatic increase in the amount of bandwidth provided by a single optical fiber.
DWDM evolved from WDM (wave division multiplexing), which began as a dual-channel 1310/1550 nanometer (nm) system. Originally, this approach led to doubling of traffic capacity. DWDM increases the channel density up to 40 separate optical wavelengths, thus significantly increasing the net fiber capacity.
For a fiber optic network architecture using DWDM, it is necessary to route and switch optical signals based on their wavelength in order to optimize data traffic usage. Dropping signal from and adding signals back to the optical network is a rudimentary building block for an optical network architecture. FIG. 1 illustrates the functionality and building elements for a conventional Add-Drop Module (AMD) 100. As an example, four wavelengths .lambda..sub.1, .lambda..sub.2, .lambda..sub.3 and .lambda..sub.4 carried along the input port 101 arrive at the Add-Drop Module 100. The AMD consists of two optical switches, 111 and 112, and two Wavelength Division Multiplexers (WDM) 111, 112. In the normal ( default ) operation, the switch 111 and switch 112 are connected to the DROP WDM 121 and Add WDM 122, respectively. The wavelength .lambda..sub.2 passes through the WDM 121 and arrive at the Drop port 131. The remaining three wavelengths, .lambda..sub.1, .lambda..sub.3 and .lambda..sub.4 are reflected by the WDM 121 and reflected again by WDM 122. Then these three wavelengths are directed to the Output Port 135 by the switch 122. Meanwhile, a new data signal in the same wavelength of .lambda..sub.2 ' transmitted from Add Port 132 is added back to the network through port 132 and WDM 122 and appears at Output Port 135.
In the faulty case such as failure of Receiver or Transmitter in the Add-Drop ports, the two switches are toggled to be connected to the Express Path 125. In this case the incoming light stream flows through the ADM 100 without interruption.
While the above-described Add-Drop module 100 may be satisfactory for some optical network applications, with the continual reduction in size of optical components in optical network applications, it may be desirable to provide an Add-Drop module which is smaller, cheaper and with better performance. The present invention reduce the numbers of components and cost in an Add-Drop module and further improve its optical performance in insertion loss.